Hollow polymeric-alkaline earth metal oxide composite

ABSTRACT

The invention provides a plurality of polymeric particles embedded with alkaline-earth metal oxide. The gas-filled polymeric microelements have a shell and a density of 5 g/liter to 200 g/liter. The shell has an outer surface and a diameter of 5 μm to 200 μm with the outer surface of the shell of the gas-filled polymeric particles having alkaline-earth metal oxide-containing particles embedded in the polymer. The alkaline-earth metal oxide-containing particles have an average particle size of 0.01 to 3 μm distributed within each of the polymeric microelements to coat less than 50 percent of the outer surface of the polymeric microelements.

BACKGROUND OF THE INVENTION

The present invention relates to polishing pads for chemical mechanicalpolishing (CMP), and in particular relates to polymeric compositepolishing pads suitable for polishing at least one of semiconductor,magnetic or optical substrates.

Semiconductor wafers having integrated circuits fabricated thereon mustbe polished to provide an ultra-smooth and flat surface that must varyin a given plane by less than a fraction of a micron. This polishing isusually accomplished in a chemical-mechanical polishing (CMP) operation.These “CMP” operations utilize chemically active slurry that is buffedagainst the wafer surface by a polishing pad. The combination of thechemically active slurry and polishing pad combine to polish orplanarize a wafer surface.

One problem associated with the CMP operation is wafer scratching.Certain polishing pads can contain foreign materials that result ingouging or scratching of the wafer. For example, the foreign materialcan result in chatter marks in hard materials, such as TEOS dielectrics.For purposes of this specification, TEOS represents the hard glass-likedielectric formed from the decomposition of tetraethyloxysilicates. Thisdamage to the dielectric can result in wafer defects and lower waferyield. Another scratching issue associated with foreign materials is thedamaging of nonferrous interconnects, such as copper interconnects. Ifthe pad scratches too deep into the interconnect line, the resistance ofthe line increases to a point where the semiconductor will not functionproperly. In extreme cases, these foreign materials createmacro-scratches that can result in the scrapping of an entire wafer.

Reinhardt et al., in U.S. Pat. No. 5,572,362, describe a polishing padthat replaces glass spheres with hollow polymeric microelements tocreate porosity within a polymeric matrix. The advantages of this designinclude uniform polishing, low defectivity and enhanced removal rate.The IC1000™ polishing pad design of Reinhardt et al. outperformed theearlier IC60 polishing pad for scratching by replacing the glass shellwith a polymeric shell. In addition, Reinhardt et al. discovered anunexpected maintenance in planarization efficiency associated withreplacing hard glass spheres with softer polymeric microspheres. Thepolishing pads of Reinhardt et al. have long served as the industrystandard for CMP polishing and continue to serve an important role inadvanced CMP applications.

Another set of problems associated with the CMP operation are pad-to-padvariability, such as density variation and within pad variation. Toaddress these problems polishing pad manufacturers have relied uponcareful casting techniques with controlled curing cycles. These effortshave concentrated on the macro-properties of the pad, but did notaddress the micro-polishing aspects associated with polishing padmaterials.

There is an industry desire for polishing pads that provide an improvedcombination of planarization, removal rate and scratching. In addition,there remains a demand for a polishing pad that provides theseproperties in a polishing pad with less pad-to-pad variability.

STATEMENT OF THE INVENTION

An aspect of the invention, includes the following: a plurality ofpolymeric particles embedded with alkaline-earth metal oxide comprising:gas-filled polymeric microelements, the gas-filled polymericmicroelements having a shell and a density of 5 g/liter to 200 g/liter,the shell having an outer surface and a diameter of 5 μm to 200 μm andthe outer surface of the shell of the gas-filled polymeric particleshaving alkaline-earth metal oxide-containing particles embedded in thepolymer, the alkaline-earth metal oxide-containing particles having anaverage particle size of 0.01 to 3 μm; the alkaline-earth metaloxide-containing particles distributed within each of the polymericmicroelements, the alkaline-earth metal oxide-containing regions beingspaced to coat less than 50 percent of the outer surface of thepolymeric microelements; and less than 0.1 weight percent total of thepolymeric microelements being associated with i) alkaline-earth metaloxide-containing particles having a particle size of greater than 5 μm;ii) alkaline-earth metal oxide-containing regions covering greater than50 percent of the outer surface of the polymeric microelements; and iii)polymeric microelements agglomerated with alkaline-earth metaloxide-containing particles to an average cluster size of greater than120 μm.

Another aspect of the invention includes the following: a plurality ofpolymeric particles embedded with alkaline-earth metal oxide comprising:gas-filled polymeric microelements, the gas-filled polymericmicroelements having a shell and a density of 10 g/liter to 100 g/liter,the shell having an outer surface and a diameter of 5 μM to 200 μm andthe outer surface of the shell of the gas-filled polymeric particleshaving alkaline-earth metal oxide-containing particles embedded in thepolymer, the alkaline-earth metal oxide-containing particles having anaverage particle size of 0.01 to 2 μm; the alkaline-earth metaloxide-containing particles distributed within each of the polymericmicroelements, the alkaline-earth metal oxide-containing regions beingspaced to coat 1 to 40 percent of the outer surface of the polymericmicroelements; and less than 0.1 weight percent total of the polymericmicroelements being associated with i) alkaline-earth metaloxide-containing particles having a particle size of greater than 5 μm;ii) alkaline-earth metal oxide-containing regions covering greater than50 percent of the outer surface of the polymeric microelements; and iii)polymeric microelements agglomerated with alkaline-earth metaloxide-containing particles to an average cluster size of greater than120 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A represents a schematic side-view-cross-section of a Coanda blockair classifier.

FIG. 1B represents a schematic front-view-cross-section of a Coandablock air classifier.

FIG. 2 is a 1,500×SEM of polyacrylonitrile/methacrylonitrile shellsembedded with magnesium-calcium oxide particles.

FIG. 3 is a 100×SEM of fine polyacrylonitrile/methacrylonitrile shellscoated with magnesium-calcium oxide particles.

FIG. 4 is a 100×SEM of polyacrylonitrile/methacrylonitrile shellsembedded with magnesium-calcium oxide particles after separation of thefine and coarse fractions.

FIG. 5 is a 100×SEM of polyacrylonitrile/methacrylonitrile shellagglomerates and rice-shaped magnesium-calcium oxide particles.

FIG. 6 is a plot of pad density versus location for polishing padscontaining poly(vinylidenedichloride)/polyacrylonitrile/silica andpolyacrylonitrile/methacrylonitrile/magnesium-calcium oxide shells.

FIG. 7 is a 250×SEM of containingpoly(vinylidenedichloride)/polyacrylonitrile/silica shells in apolyurethane matrix.

FIG. 8 is a 250×SEM ofpolyacrylonitrile/methacrylonitrile/magnesium-calcium oxide shells in apolyurethane matrix.

FIG. 9 is a 250×SEM ofpoly(vinylidenedichloride)/polyacrylonitrile/silica shells in apolyurethane matrix after skiving.

FIG. 10 is a 250×SEM ofpolyacrylonitrile/methacrylonitrile/magnesium-calcium oxide shells in apolyurethane matrix after skiving.

FIG. 11 is a shear modulus plot for Comparative Examples B and C andExample 10.

FIG. 12 is a plot illustrating toughness for pads containing no shells,poly(vinylidenedichloride)/polyacrylonitrile/silica andpolyacrylonitrile/methacrylonitrile/magnesium-calcium oxide shells.

FIG. 13 is a 250×SEM illustrating the fracture morphology forComparative Example C.

FIG. 14 is a 250×SEM illustrating the fracture morphology for Example10.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method for forming a composite alkaline earthmetal oxide-containing polishing pad useful for polishing semiconductorsubstrates. The polishing pad includes a polymeric matrix, hollowpolymeric microelements and alkaline earth metal oxide-containingparticles embedded in the polymeric microelements. The alkaline earthelement is preferably calcium oxide, magnesium oxide or a mixture ofmagnesium and calcium oxides. Surprisingly, the alkaline earth metaloxide-containing particles do not tend to result in excessive scratchingor gouging for advanced CMP applications when classified to a specificstructure associated with polymeric microelements. This limited gougingand scratching occurs despite the polymeric matrix having alkaline earthmetal oxide-containing particles at its polishing surface.

Typical polymeric polishing pad matrix materials include polycarbonate,polysulfone, polyamides, ethylene copolymers, polyethers, polyesters,polyether-polyester copolymers, acrylic polymers, polymethylmethacrylate, polyvinyl chloride, polycarbonate, polyethylenecopolymers, polybutadiene, polyethylene imine, polyurethanes, polyethersulfone, polyether imide, polyketones, epoxies, silicones, copolymersthereof and mixtures thereof. Preferably, the polymeric material is apolyurethane; and may be either a cross-linked a non-cross-linkedpolyurethane. For purposes of this specification, “polyurethanes” areproducts derived from difunctional or polyfunctional isocyanates, e.g.polyetherureas, polyisocyanurates, polyurethanes, polyureas,polyurethaneureas, copolymers thereof and mixtures thereof.

Preferably, the polymeric material is a block or segmented copolymercapable of separating into phases rich in one or more blocks or segmentsof the copolymer. Most preferably, the polymeric material is apolyurethane. Cast polyurethane matrix materials are particularlysuitable for planarizing semiconductor, optical and magnetic substrates.An approach for controlling a pad's polishing properties is to alter itschemical composition. In addition, the choice of raw materials andmanufacturing process affects the polymer morphology and the finalproperties of the material used to make polishing pads.

Preferably, urethane production involves the preparation of anisocyanate-terminated urethane prepolymer from a polyfunctional aromaticisocyanate and a prepolymer polyol. For purposes of this specification,the term prepolymer polyol includes diols, polyols, polyol-diols,copolymers thereof and mixtures thereof. Preferably, the prepolymerpolyol is selected from the group comprising polytetramethylene etherglycol [PTMEG], polypropylene ether glycol [PPG], ester-based polyols,such as ethylene or butylene adipates, copolymers thereof and mixturesthereof. Example polyfunctional aromatic isocyanates include 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, 4,4′-diphenylmethanediisocyanate, naphthalene-1,5-diisocyanate, tolidine diisocyanate,para-phenylene diisocyanate, xylylene diisocyanate and mixtures thereof.The polyfunctional aromatic isocyanate contains less than 20 weightpercent aliphatic isocyanates, such as 4,4′-dicyclohexylmethanediisocyanate, isophorone diisocyanate and cyclohexanediisocyanate.Preferably, the polyfunctional aromatic isocyanate contains less than 15weight percent aliphatic isocyanates and more preferably, less than 12weight percent aliphatic isocyanate.

Example prepolymer polyols include polyether polyols, such as,poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and mixturesthereof, polycarbonate polyols, polyester polyols, polycaprolactonepolyols and mixtures thereof. Example polyols can be mixed with lowmolecular weight polyols, including ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol,2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol,1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, diethyleneglycol, dipropylene glycol, tripropylene glycol and mixtures thereof.

Preferably the prepolymer polyol is selected from the group comprisingpolytetramethylene ether glycol, polyester polyols, polypropylene etherglycols, polycaprolactone polyols, copolymers thereof and mixturesthereof. If the prepolymer polyol is PTMEG, copolymer thereof or amixture thereof, then the isocyanate-terminated reaction productpreferably has a weight percent unreacted NCO range of 8.0 to 20.0weight percent. For polyurethanes formed with PTMEG or PTMEG blendedwith PPG, the preferable weight percent NCO is a range of 8.75 to 12.0;and most preferably it is 8.75 to 10.0. Particular examples of PTMEGfamily polyols are as follows: Terathane® 2900, 2000, 1800, 1400, 1000,650 and 250 from Invista; Polymeg® 2900, 2000, 1000, 650 from Lyondell;PolyTHF® 650, 1000, 2000 from BASF, and lower molecular weight speciessuch as 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. If theprepolymer polyol is a PPG, copolymer thereof or a mixture thereof, thenthe isocyanate-terminated reaction product most preferably has a weightpercent unreacted NCO range of 7.9 to 15.0 wt. %. Particular examples ofPPG polyols are as follows: Arcol® PPG-425, 725, 1000, 1025, 2000, 2025,3025 and 4000 from Bayer; Voranol® 1010L, 2000L, and P400 from Dow;Desmophen® 1110BD, Acclaim® Polyol 12200, 8200, 6300, 4200, 2200 bothproduct lines from Bayer. If the prepolymer polyol is an ester,copolymer thereof or a mixture thereof, then the isocyanate-terminatedreaction product most preferably has a weight percent unreacted NCOrange of 6.5 to 13.0. Particular examples of ester polyols are asfollows: Millester 1, 11, 2, 23, 132, 231, 272, 4, 5, 510, 51, 7, 8, 9,10, 16, 253, from Polyurethane Specialties Company, Inc.; Desmophen®1700, 1800, 2000, 2001KS, 2001K², 2500, 2501, 2505, 2601, PE65B fromBayer; Rucoflex 5-1021-70, S-1043-46, S-1043-55 from Bayer.

Typically, the prepolymer reaction product is reacted or cured with acurative polyol, polyamine, alcohol amine or mixture thereof. Forpurposes of this specification, polyamines include diamines and othermultifunctional amines. Example curative polyamines include aromaticdiamines or polyamines, such as, 4,4′-methylene-bis-o-chloroaniline[MBCA], 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) [MCDEA];dimethylthiotoluenediamine; trimethyleneglycol di-p-aminobenzoate;polytetramethyleneoxide di-p-aminobenzoate; polytetramethyleneoxidemono-p-aminobenzoate; polypropyleneoxide di-p-aminobenzoate;polypropyleneoxide mono-p-aminobenzoate;1,2-bis(2-aminophenylthio)ethane; 4,4′-methylene-bis-aniline;diethyltoluenediamine; 5-tert-butyl-2,4- and3-tert-butyl-2,6-toluenediamine; 5-tert-amyl-2,4- and3-tert-amyl-2,6-toluenediamine and chlorotoluenediamine. Optionally, itis possible to manufacture urethane polymers for polishing pads with asingle mixing step that avoids the use of prepolymers.

The components of the polymer used to make the polishing pad arepreferably chosen so that the resulting pad morphology is stable andeasily reproducible. For example, when mixing4,4′-methylene-bis-o-chloroaniline [MBCA] with diisocyanate to formpolyurethane polymers, it is often advantageous to control levels ofmonoamine, diamine and triamine. Controlling the proportion of mono-,di- and triamines contributes to maintaining the chemical ratio andresulting polymer molecular weight within a consistent range. Inaddition, it is often important to control additives such asanti-oxidizing agents, and impurities such as water for consistentmanufacturing. For example, since water reacts with isocyanate to formgaseous carbon dioxide, controlling the water concentration can affectthe concentration of carbon dioxide bubbles that form pores in thepolymeric matrix. Isocyanate reaction with adventitious water alsoreduces the available isocyanate for reacting with chain extender, sochanges the stoichiometry along with level of crosslinking (if there isan excess of isocyanate groups) and resulting polymer molecular weight.

The polyurethane polymeric material is preferably formed from aprepolymer reaction product of toluene diisocyanate andpolytetramethylene ether glycol with an aromatic diamine. Mostpreferably the aromatic diamine is 4,4′-methylene-bis-o-chloroaniline or4,4′-methylene-bis-(3-chloro-2,6-diethylaniline). Preferably, theprepolymer reaction product has a 6.5 to 15.0 weight percent unreactedNCO. Examples of suitable prepolymers within this unreacted NCO rangeinclude: Imuthane® prepolymers PET-70D, PHP-70D, PET-75D, PHP-75D,PPT-75D, PHP-80D manufactured by COIM USA, Inc. and Adiprene®prepolymers, LFG740D, LF700D, LF750D, LF751D, LF753D, L325 manufacturedby Chemtura. In addition, blends of other prepolymers besides thoselisted above could be used to reach to appropriate percent unreacted NCOlevels as a result of blending. Many of the above-listed prepolymers,such as, LFG740D, LF700D, LF750D, LF751D, and LF753D are low-freeisocyanate prepolymers that have less than 0.1 weight percent free TDImonomer and have a more consistent prepolymer molecular weightdistribution than conventional prepolymers, and so facilitate formingpolishing pads with excellent polishing characteristics. This improvedprepolymer molecular weight consistency and low free isocyanate monomergive a more regular polymer structure, and contribute to improvedpolishing pad consistency. For most prepolymers, the low free isocyanatemonomer is preferably below 0.5 weight percent. Furthermore,“conventional” prepolymers that typically have higher levels of reaction(i.e. more than one polyol capped by a diisocyanate on each end) andhigher levels of free toluene diisocyanate prepolymer should producesimilar results. In addition, low molecular weight polyol additives,such as, diethylene glycol, butanediol and tripropylene glycolfacilitate control of the prepolymer reaction product's weight percentunreacted NCO.

Similarly, the polyurethane polymeric material may be formed from aprepolymer reaction product of 4,4′-diphenylmethane diisocyanate (MDI)and polytetramethylene glycol with a diol. Most preferably, the diol is1,4-butanediol (BDO). Preferably, the prepolymer reaction product has 6to 13 wt % unreacted NCO. Examples of suitable polymers with thisunreacted NCO range include the following: Imuthane 27-85A, 27-90A,27-95A, 27-52D, 27-58D from COIM USA and Andur® IE-75AP, IE80AP, IE90AP,IE98AP, IE110AP prepolymers from Anderson Development Company.

In addition to controlling weight percent unreacted NCO, the curativeand prepolymer reaction product typically has an OH or NH₂ to unreactedNCO stoichiometric ratio of 85 to 115 percent, preferably 90 to 100percent. This stoichiometry could be achieved either directly, byproviding the stoichiometric levels of the raw materials, or indirectlyby reacting some of the NCO with water either purposely or by exposureto adventitious moisture.

The polymeric matrix contains polymeric microelements distributed withinthe polymeric matrix and at the polishing surface of the polymericmatrix. The polymeric microelements have an outer surface and arefluid-filled for creating texture at the polishing surface. The fluidfilling the matrix can be a liquid or a gas. If the fluid is a liquid,then the preferred fluid is water, such as distilled water that onlycontains incidental impurities. If the fluid is a gas, then air,nitrogen, argon, carbon dioxide or combination thereof is preferred. Forsome microelements, the gas may be an organic gas, such as isobutane.The gas-filled polymeric microelements typically have an average size of5 to 200 microns. Preferably, the gas-filled polymeric microelementstypically have an average size of 10 to 100 microns. Most preferably,the gas-filled polymeric microelements typically have an average size of10 to 80 microns. Although not necessary, the polymeric microelementspreferably have a spherical shape or represent microspheres. Thus, whenthe microelements are spherical, the average size ranges also representdiameter ranges. For example, average diameter ranges of 5 to 200microns, preferably 10 to 100 microns and most preferably 10 to 80microns.

The polishing pad contains alkaline earth (Group IIA of the PeriodicTable) metal oxide-containing regions distributed within each of thepolymeric microelements. These alkaline earth metal oxide-containingregions may be particles or have an elongated alkaline earth metaloxide-containing structure. Typically, the alkaline earth metaloxide-containing regions represent particles embedded or attached to thepolymeric microelements. The average particle size of the alkaline earthmetal oxide-containing particles is typically 0.01 to 3 μm. Preferably,the average particle size of the alkaline earth metal oxide-containingparticles is 0.01 to 2 μm. These alkaline earth metal oxide-containingparticles are spaced to coat less than 50 percent of the outer surfaceof the polymeric microelements. Preferably, the alkaline earth metaloxide-containing regions cover 1 to 40 percent of the surface area ofthe polymeric microelements. Most preferably, the alkaline earth metaloxide-containing regions cover 2 to 30 percent of the surface area ofthe polymeric microelements. The alkaline earth metal oxide-containingmicroelements have a density of 5 g/liter to 200 gaiter. Typically, thealkaline earth metal oxide-containing microelements have a density of 10g/liter to 100 g/liter.

In order to avoid increased scratching or gouging, it is important toavoid alkaline earth metal oxide-containing particles withdisadvantageous structure or morphology. These disadvantageous alkalineearth metal oxide-containing particles should total less than 0.1 weightpercent total of the polymeric microelements. Preferably, thesedisadvantageous alkaline earth metal oxide-containing particles shouldtotal less than 0.05 weight percent total of the polymericmicroelements. The first type of disadvantageous alkaline earth metaloxide-containing particles is alkaline earth metal oxide-containingparticles having a particle size of greater than 5 μm. These alkalineearth metal oxide-containing particles are known to result in chatterdefects in TEOS wafers, and scratch and gouge defects in copperinterconnects. The second type of disadvantageous alkaline earth metaloxide-containing particles is alkaline earth metal oxide-containingregions covering greater than 50 percent of the outer surface of thepolymeric microelements. These microelements containing a large alkalineearth metal oxide-containing surface area also can scratch wafers ordislodge with the microelements to result in chatter defects in TEOSwafers, and scratch and gouge defects in copper interconnects. The thirdtype of disadvantageous alkaline earth metal oxide-containing particlesis agglomerates. Specifically, polymeric microelements can agglomeratewith alkaline earth metal oxide-containing particles to an averagecluster size of greater than 120 μm. The 120 μm agglomeration size istypical for microelements having an average diameter of about 40 μm.Larger microelements will form larger agglomerates. Alkaline earth metaloxide-containing particles with this morphology can result in visualdefects and scratching defects with sensitive polishing operations.

Air classification can be useful to produce the composite alkaline earthmetal oxide-containing polymeric microelements with minimaldisadvantageous alkaline earth metal oxide-containing particle species.Unfortunately, alkaline earth metal oxide-containing polymericmicroelements often have variable density, variable wall thickness andvariable particle size. In addition, the polymeric microelements havevaried alkaline earth metal oxide-containing regions distributed ontheir outer surfaces. Thus, separating polymeric microelements withvarious wall thicknesses, particle size and density has multiplechallenges and multiple attempts at centrifugal air classification andparticle screening failed. These processes are useful for at bestremoving one disadvantageous ingredient from the feedstock, such asfines. For example, because much of the alkaline earth metaloxide-containing microspheres have the same size as the desirousalkaline earth metal oxide-containing composite, it is difficult toseparate these using screening methods. It has been discovered, however,that separators that operate with a combination of inertia, gas or airflow resistance and the Coanda effect can provide effective results. TheCoanda effect states that if a wall is placed on one side of a jet, thenthat jet will tend to flow along the wall. Specifically, passinggas-filled microelements in a gas jet adjacent a curved wall of a Coandablock separates the polymeric microelements. The coarse polymericmicroelements separate from the curved wall of the Coanda block to cleanthe polymeric microelements in a two-way separation. When the feed stockincludes alkaline earth metal oxide-containing fines, the process mayinclude the additional step of separating the polymeric microelementsfrom the alkaline earth metal oxide-containing fines with the wall ofthe Coanda block with the fines following the Coanda block. In athree-way separation, coarse separates the greatest distance from theCoanda block, the middle or cleaned cut separates an intermediatedistance and the fines follow the Coanda block. The Matsubo Corporationmanufactures elbow-jet air classifiers that take advantage of thesefeatures for effective particle separation. In addition to the feedstockjet, the Matsubo separators provide an additional step of directing twoadditional gas streams into the polymeric microelements to facilitateseparating the polymeric microelements from the coarse particlesassociated with polymeric microelements.

The separating of the alkaline earth metal oxide-containing particlefines and coarse particles associated with the polymeric microelementsadvantageously occurs in a single step. Although a single pass iseffective for removing both coarse and fine materials, it is possible torepeat the separation through various sequences, such as first coarsepass, second coarse and then first fine pass and second fine pass.Typically, the cleanest results, however, originate from two orthree-way separations. The disadvantages of additional three-wayseparations are yield and cost. The feed stock typically containsgreater than 0.1 weight percent disadvantageous alkaline earth metaloxide-containing particles. Furthermore, it is effective with greaterthan 0.2 weight percent and greater than 1 weight percentdisadvantageous alkaline earth metal oxide-containing particlefeedstocks.

After separating out or cleaning the polymeric microelements, insertingthe polymeric microelements into a liquid polymeric matrix forms thepolishing pad. The typical means for inserting the polymericmicroelements into the pad include casting, extrusion, aqueous-solventsubstitution and aqueous dispersion polymers. Mixing improves thedistribution of the polymeric microelements in a liquid polymer matrix.After mixing, drying or curing the polymer matrix forms the polishingpad suitable for grooving, perforating or other polishing pad finishingoperations.

Referring to FIGS. 1A and 1B, the elbow-jet air classifier has width “w”between two sidewalls. Air or other suitable gas, such as carbondioxide, nitrogen or argon flows through openings 10, 20 and 30 tocreate a jet-flow around Coanda block 40. Injecting polymericmicroelements with a feeder 50, such as a pump or vibratory feeder,places the polymeric microelements in a jet stream that initiates theclassification process. In the jet stream the forces of inertia, drag(or gas flow resistance) and the Coanda effect combine to separate theparticles into three classifications. The fines 60 follow the Coandablock. The medium sized alkaline-earth metal oxide-containing particleshave sufficient inertia to overcome the Coanda effect for collection ascleaned product 70. Finally, the coarse particles 80 travel the greatestdistance for separation from the medium particles. The coarse particlescontain a combination of i) alkaline earth metal oxide-containingparticles having a particle size of greater than 5 μm; ii) alkalineearth metal oxide-containing regions covering greater than 50 percent ofthe outer surface of the polymeric microelements; and iii) polymericmicroelements agglomerated with alkaline earth metal oxide-containingparticles to an average cluster size of greater than 120 μm. Thesecoarse particles tend to have negative impacts on wafer polishing andespecially patterned wafer polishing for advanced nodes. The spacing orwidth of the separator determines the fraction separated into eachclassification. Alternatively, it is possible to close the finecollector to separate the polymeric microelements into two fractions, acoarse fraction and a cleaned fraction.

EXAMPLES Separation

An Elbow-Jet air classifier (Model EJ15-3S) from Matsubo Corporationprovided separation of a sample of isopentane-filled copolymer ofpolyacrylonitrile and methacrylonitrile having an average diameter of 40microns and a density of 30 g/liter. These hollow microspheres containedmagnesium-calcium oxide-containing particles embedded in the copolymer.The magnesium-calcium oxide-containing particles covered approximately 5to 15 percent of the outer surface area of the microspheres. Inaddition, the sample contained copolymer microspheres associated withmagnesium-calcium oxide particles having a particle size of greater than5 μm; ii) magnesium-calcium oxide-containing regions covering greaterthan 50 percent of the outer surface of the polymeric microelements; andiii) polymeric microelements agglomerated with magnesium-calciumoxide-containing particles to an average cluster size of greater than120 μm. The Elbow-Jet classifier contained a Coanda block and thestructure of FIGS. 1A and 1B. FIG. 2 illustrates desirablemagnesium-calcium oxide-containing microspheres in the presence of fineparticles. For the desirable microspheres, the white regions representmagnesium oxide-calcium oxide mineral particles embedded in the polymershell. For the undesirable particles, the white region covers greaterthan half the particle or coats the entire particle. Feeding thepolymeric microspheres through a vibratory feeder into the gas jet withselected settings produced the results of Table 1.

TABLE 1 Ejector Air Feed Edge Position Yield Exam- Edge Pressure Rate F 

 R M 

 R F M [g] G [g] ple Type [MPa] kg/hr [mm] [mm] [%] [%] [%] 1 LE 0.301.06 7.0 25.0 32.2 67.4 0.4 50G 2 LE 0.30 0.88 5.0 20.0 10.2 89.6 0.250G 3 LE 0.30 0.75 3.0 20.0 4.8 94.9 0.3 50G 4 LE 0.30 0.50 7.0 15.050.6 31.6 17.8 50G 5 LE 0.30 1.05 5.0 20.0 13.5 86.1 0.4 50G 6 LE 0.301.12 7.0 25.0 20.4 79.4 0.2 50G 7 LE 0.30 0.83 4.0 20.0 7.0 92.8 0.2 50G8 LE 0.30 0.92 4.0 20.0 8.7 90.6 0.7 50G

The data of Table 1 show effective removal of fines [F] and coarse [G]materials. Example 7 provided 7 weight percent fines and 0.2 weightpercent coarse material. Example 8, an extended run of Example 7,produced 8.7 weight percent fines and 0.7 weight percent coarse. Thecoarse material contained copolymer microspheres associated withmagnesium-calcium oxide-containing particles having a particle size ofgreater than 5 μm; ii) magnesium-calcium oxide-containing regionscovering greater than 50 percent of the outer surface of the polymericmicroelements; and iii) polymeric microelements agglomerated withmagnesium-calcium oxide-containing particles to an average cluster sizeof greater than 120 μm.

Referring to FIGS. 3 to 5, FIG. 3 illustrates the fines [F], FIG. 4illustrates the cleaned magnesium-calcium oxide-containing polymericmicrospheres [M] and FIG. 5 illustrates the coarse [G] from theconditions of Examples 7 and 8. The fines appear to have a sizedistribution that contains only a minor fraction of medium-sizedpolymeric microelements. The coarse cut contains visible microelementagglomerates and polymeric microelements that have magnesium-calciumoxide-containing regions covering greater than 50 percent of their outersurfaces. The mid cut appears clear of most of the fine and coarsepolymeric microelements. These SEM micrographs illustrate the dramaticdifference achieved with the classification into three segments.

Effect on Pad Density

Table 2 provides microsphere formulations for casting polyurethane cakesused to make polishing pads:

TABLE 2 Polishing Pad Ingredients and Formulations Shell Wall TgDiameter Wt % Example Microsphere (° C.) (μm) Microspheres APoly(vinylidene- 96 40 1.57 dichloride)/ Polyacrylonitrile/ Silica 9Polyacrylonitrile/ 116 40 1.34 Methacrylonitrile/ Magnesium- CalciumOxide

Polyurethane cakes were prepared by controlled mixing of anisocyanate-terminated urethane prepolymer (Adiprene® L325, 9.1% NCO,from Chemtura Corporation) with 4,4′-methylene-bis-o-chloroaniline(MBCA) as the curative. Prepolymer and curative temperatures were 51 and116° C., respectively. The ratio of prepolymer to curative was set suchthat the stoichiometry, as defined by the percent ratio of NH₂ groups inthe curative to NCO groups in the prepolymer, was 87%. Theseformulations illustrate the effects of the addition of different polymermicrospheres to a hard polymer matrix. Specifically, without addedpolymeric microspheres the hardness of the Adiprene L325/MBOCA polymermatrix is 72 Shore D; and with the level of polymeric microspheres addedin the above examples the hardness drops to 55 to 60D Shore D.

Porosity was introduced into the formulations by adding microspheressuch that the average density of pads from Comparative Examples A andExample B would be equivalent. In Comparative Example A,poly(vinylidenedichloride)/polyacrylonitrile shell walls interspersedwith silica particles was used as the pore formation agent. For Example1, polyacrylonitrile/methacrylonitrile shell walls interspersed withmagnesium-calcium oxide particles was used. Both shell walls had thesame average 40 micron microsphere diameter. Thepolyacrylonitrile/methacrylonitrile particles were classified prior toblending using the process technique and conditions described above.

Prepolymer, curative and microspheres were simultaneously mixed togetherusing a high shear mix-head. After exiting the mix-head, the mixedingredients were dispensed for 4 minutes into a 34 inch (86.4 cm)diameter circular mold to give a total pour thickness of approximatelytwo inches (5.1 cm). The ingredients were allowed to gel for 15 minutesbefore being placed in a curing oven and then cured with the followingcycle: 30 minutes ramp from ambient to a set point of 104° C., 15.5hours at 104° C., and 2 hours with the set point reduced to 21° C.

The molded article was then “skived” (cut using a moving blade) at atemperature between 70 and 80° C. into approximately twenty thin sheets80 mil (2.0 mm) thick. Skiving initiated from the cake's top surfacewith any incomplete sheets being discarded. (Each sheet can besubsequently converted into a polishing pad by grooving or perforatingmacro-texture into its surface and laminating to a compressiblesub-pad.)

The density of each sheet was determined by measuring its weight,thickness and diameter in accordance with ASTM Standard D1622. FIG. 6shows the density of each sheet from the top to the bottom of the moldedarticle.

The amount of polymeric microsphere added was adjusted to achieve thesame level of porosity and density averaged over the entire moldedarticle. For Comparative Example A and Example 1 the average density ofall the sheets for both molded articles was the same at 0.809 g/cm³.

However, since the chemical reaction between the prepolymer and curativewas exothermic, a strong temperature gradient existed through the moldedarticle, such that the bottom of the molded article was cooler than themiddle or top regions. Exotherm temperatures for thisprepolymer-curative combination exceeded the softening temperature (Tg)of the shell wall. Since these temperatures were achieved while themolded article was still gelling, the polymeric microsphere particlesincreased in diameter in response to the higher temperatures and aporosity profile developed within the molded article. This profile waspronounced in relation to the cooler bottom sheets cut from the moldedarticle. The bottom layer sheets had higher densities than the rest ofthe sheets and may be out of specification causing them to be rejectedand manufacturing yields decreased. Advantageously, all pads have adensity or specific gravity within 5%. Most advantageously, it ispossible to remove pads to leave all pads with a density or specificgravity that varies less than 2%.

In FIG. 6, Comparative Example A clearly illustrates the problem. Whenpoly(vinylidenedichloride)/polyacrylonitrile was used as the poreformation agent, the density of the bottom layers were significantlyhigher than the targeted mean density value and must be rejected. Incontrast, when polyacrylonitrile/methacrylonitrile is substituted in thesame polymeric matrix formulation (Example 9), density variation fromthe top to the bottom of the cake is significantly reduced and yieldsfor out of specification density values greatly reduced. The enhancedperformance of the polyacrylonitrile/methacrylonitrile microspheres overpoly(vinylidenedichloride)/polyacrylonitrile appear to be a directconsequence of their higher shell wall softening temperature. Asdiscussed previously and shown in Table 2, Tg of thepolyacrylonitrile/methacrylonitrile microspheres was 20° C. higher thanthat of poly(vinylidenedichloride)/polyacrylonitrile microspheres,effectively reducing their tendency to expand in response to highexotherm temperatures. The polyacrylonitrile/methacrylonitrile shellsprovided the additional advantage of being a chlorine-free polymer.

FIGS. 7 and 8 show SEM cross-sections of sheets of Comparative Example Aand Example 9, respectively. A comparison of FIGS. 7 and 8 shows thatthe pore sizes are very similar. The figures also show in both casesthat the microspheres are uniformly distributed throughout the polymermatrix. A subtle difference between the two figures is the presence ofmore shell wall fragments present for thepolyacrylonitrile/methacrylonitrile microspheres. This is indicative ofa less elastic and more brittle shell wall.

Skiving Comparison

The difference is more pronounced for skived surfaces as shown in FIGS.9 and 10. The skiving operation imparts more mechanical stress and ismore likely to fracture the microspheres, especially if the shell wallsare less ductile and more brittle.

More brittle particles can break into smaller pieces during subsequentdiamond conditioning and polishing. This creates smaller polishingdebris. Smaller polishing debris is less likely to scratch semiconductorwafers and result in fatal defects that could render the wafer beingpolished useless.

The surface roughness of the skived surfaces shown in FIGS. 9 and 10were measured by a contact method using a Zeiss Profileometer (ModelSurfcom 1500). A two micron tip diamond stylus (DM43801) was trackedacross the pad surface and key surface roughness parameters determined.These included the average surface roughness (Ra), reduced peak height(Rpk), core roughness depth (Rk) and reduced valley depth (Rvk), asdefined in “Introduction to Surface Roughness and Scattering” by Bennettand Mattsson.

Roughness values for Comparative Examples A and Example 1 are tabulatedin Table 3:

TABLE 3 Surface Roughness Measurements Roughness Parameters (microns)Example Ra Rpk Rk Rvk A  9.6 ± 0.2  7.0 ± 1.3 22.4 ± 0.3 22.2 ± 1.6 910.9 ± 0.5 14.8 ± 0.8 29.1 ± 4.0 22.3 ± 1.0

All roughness parameters were higher for the pad containing thepolyacrylonitrile/methacrylonitrile microspheres. Typically, a highersurface roughness results in higher removal rates during polishing andhence increased wafer throughput.

Effect of Microelement on Pad Properties in Soft Formulations

The next examples illustrate the effect of adding either 40 microndiameter poly(vinylidenedichloride)/polyacrylonitrile orpolyacrylonitrile/methacrylonitrile microspheres to a much softermatrix. Formulations and processing conditions are summarized in Table4:

TABLE 4 Pad Formulations Formulation Example B Example C Example 10Prepolymer Imuthane ® Imuthane ® Imuthane ® 27-95A 27-95A 27-95A % NCO9.06 9.06 9.06 Weight of 250 250 250 Prepolymer (g) Weight Curative 23.423.2 23.3 (Butane diol) (g) Curative 45 45 45 Equivalent WeightStoichiometry 96 96 96 (OH/NCO) (%) Microsphere None poly(vinylidene-polyacrylonitrile/ dichloride)/poly- methacrylonitrile/acrylonitrile/silica magnesium- calcium oxide Weight % 0.00 2.00 2.00Microsphere Weight of 0.00 5.00 5.00 Microsphere (g) Volume % 0 40 40Porosity in Pad Catalyst Dabco 33-LV Dabco 33-LV Dabco 33-LV CatalystWeight 0.210 0.210 0.210 % wrt Curative Prepolymer 80 80 80 Temperature(° C.) Curative 80 80 80 Temperature (° C.) Aluminum Mold 115 115 115Temperature (° C.) Degas Pre- Yes Yes Yes polymer and Curative VortexMix Time 30 30 30 (sec) Curing cycle 16 hrs at 16 hrs at 16 hrs at 115°C. 115° C. 115° C. Total Gel-time at 4:28 4:01 2:52 115° C. (m:s)

In these formulations, the prepolymer (Imuthane® 27-95A from COIM USAInc.) used was polyether-based terminated with 4,4′-diphenylmethanediisocyanate (MDI) and cured with 1,4-butanediol. A small amount ofamine catalyst (Dabco® 33-LV from Air Products) was used to acceleratethe urethane reaction. These formulations were made in the laboratoryusing a vortex mixer to thoroughly mix the prepolymer, curative andmicrospheres together. After mixing, these were poured into aluminummolds and cured at elevated temperature to form sheets approximately 12cm wide by 20 cm long by 2 mm thick for physical propertycharacterization.

TABLE 5 Soft Pad Physical Properties Exam- Exam- Exam- Property TestMethod ple B ple C ple 10 Hardness (Shore D) ASTM D 2240 42.2 25.5 26.3Density (g/cm³) ASTM D 1622 1.08 0.66 0.66 Tensile Strength ASTM D41212.6 9.6 12.6 (MPa) Elongation to Break (%) ASTM D412 251 384 528Toughness (MPa) ASTM D412 23.2 25.1 40.5 100% Modulus (MPa) ASTM D4128.9 5.4 5.3 Microsphere Softening ASTM D5279 94 116 Peak Temperature (°C.) Pad Modulus (G′) at ASTM D5279 12.2 7.2 10.4 100° C. (MPa)

Addition of the polymer microspheres to the polymer reduced bothhardness and density; and from a comparison of Comparative Example C andExample 10, it is apparent that there is little difference between theadditions of either microsphere formulation.

However, the differing softening temperatures ofpoly(vinylidenedichloride)/polyacrylonitrile andpolyacrylonitrile/methacrylonitrile microspheres has an impact on padmodulus at elevated temperatures. As discussed earlier, thepolyacrylonitrile/methacrylonitrile shell had a higher softeningtemperature than the poly(vinylidenedichloride)/polyacrylonitrile shell.As shown by the dynamic mechanical data of FIG. 11, this has the effectof maintaining higher modulus values at elevated temperatures. Duringpolishing the asperity tips of the pad surface become locally heatedfrom the friction of polishing and can excessively soften. A highermodulus beneficially increases asperity life and decreases the need forthe asperities to be regenerated by diamond conditioning.

The tensile data shown in Table 5 are both unexpected and advantageous.Usually when porosity is introduced into a polymer, all tensileproperties such as modulus, tensile strength, elongation to break andtoughness decrease. This is not the case for the formulations of Table4. As expected, with the addition of the polymeric microspheres modulusdecreases. However, tensile strength only decreases for thepoly(vinylidenedichloride)/polyacrylonitrile microspheres and theaddition of either poly(vinylidenedichloride)/polyacrylonitrilemicrospheres or especially polyacrylonitrile/methacrylonitrilemicrospheres increases elongation to break and toughness values, wheretoughness is measured as the area under the stress-strain curve.Toughness values are plotted in FIG. 12.

A comparison of Comparative Examples B, C and Example 10 indicate thatthe addition of polyacrylonitrile/methacrylonitrile microspheresfavorably increases pad toughness compared to the addition ofpoly(vinylidenedichloride)/polyacrylonitrile and even with respect tothe non-porous control. This behavior suggests the microspheres are welladhered to the surrounding polymer matrix and that more energy isrequired to fracture pad formulations containingpolyacrylonitrile/methacrylonitrile microspheres.

The dog-bone samples used to obtain the tensile data were examined byscanning electron microscopy of the microspheres after fracture.Residual strain remains in the narrow section of the dog-bone aftertesting. Photographs taken perpendicular to the strain direction wereused to provide insight into the failure mode.

FIGS. 13 and 14 show failure behavior of Comparative Example C andExample 10. In neither case were voids apparent that would be consistentwith the microspheres separating from the polymer matrix. This supportsthe above suggestion that the microspheres were well adhered. However,in FIG. 14 many shell fragments are present in the pore structure. Asthe pad was stretched the well adhered microsphere shell wall alsostretched but, given its higher Tg and hence more rigid polymerstructure, the shell wall fractures but remained attached to thesurrounding polymer matrix. Since additional energy is required to breakthe shell walls, toughness values increase significantly.

The polishing pads of the invention include magnesium-calciumoxide-containing particles distributed in a consistent and uniformstructure to reduce polishing defects. In particular, the compositeparticle structure of the claimed invention can reduce gouge andscratching defects for copper polishing with cast polyurethane polishingpads. In addition, the air classification can provide a more consistentproduct with less density and within pad variation.

The invention claimed is:
 1. A plurality of polymeric particles embeddedwith alkaline-earth metal oxide comprising: gas-filled polymericmicroelements, the gas-filled polymeric microelements having a shell anda density of 5 g/liter to 200 g/liter, the shell having an outer surfaceand a diameter of 5 μm to 200 μm and the outer surface of the shell ofthe gas-filled polymeric particles having alkaline-earth metaloxide-containing particles embedded in the polymer, the alkaline-earthmetal oxide-containing particles having an average particle size of 0.01to 3 μm; the alkaline-earth metal oxide-containing particles distributedwithin each of the polymeric microelements, the alkaline-earth metaloxide-containing regions being spaced to coat less than 50 percent ofthe outer surface of the polymeric microelements; and less than 0.1weight percent total of the polymeric microelements being associatedwith i) alkaline-earth metal oxide-containing particles having aparticle size of greater than 5 μm; ii) alkaline-earth metaloxide-containing regions covering greater than 50 percent of the outersurface of the polymeric microelements; and iii) polymeric microelementsagglomerated with alkaline-earth metal oxide-containing particles to anaverage cluster size of greater than 120 μm.
 2. The plurality ofpolymeric particles of claim 1 wherein the gas-filled polymericmicroelements are a copolymer of polyacrylonitrile and methacrylonitrilefilled with isopentane.
 3. The plurality of polymeric particles of claim1 wherein the gas-filled polymeric microelements have an average size of5 to 200 microns.
 4. The plurality of polymeric particles of claim 1wherein the alkaline-earth metal oxide-containing particles cover 1 to40 percent of the outer surface of the shell of the gas-filled polymericmicroelements.
 5. A plurality of polymeric particles embedded withalkaline-earth metal oxide comprising: gas-filled polymericmicroelements, the gas-filled polymeric microelements having a shell anda density of 10 g/liter to 100 g/liter, the shell having an outersurface and a diameter of 5 μm to 200 μm and the outer surface of theshell of the gas-filled polymeric particles having alkaline-earth metaloxide-containing particles embedded in the polymer, the alkaline-earthmetal oxide-containing particles having an average particle size of 0.01to 2 μm; the alkaline-earth metal oxide-containing particles distributedwithin each of the polymeric microelements, the alkaline-earth metaloxide-containing regions being spaced to coat 1 to 40 percent of theouter surface of the polymeric microelements; and less than 0.1 weightpercent total of the polymeric microelements being associated with i)alkaline-earth metal oxide-containing particles having a particle sizeof greater than 5 μm; ii) alkaline-earth metal oxide-containing regionscovering greater than 50 percent of the outer surface of the polymericmicroelements; and iii) polymeric microelements agglomerated withalkaline-earth metal oxide-containing particles to an average clustersize of greater than 120 μm.
 6. The plurality of polymeric particles ofclaim 5 wherein the gas-filled polymeric microelements are a copolymerof polyacrylonitrile and methacrylonitrile filled with isopentane. 7.The plurality of polymeric particles of claim 5 wherein the gas-filledpolymeric microelements have an average size of 10 to 100 microns. 8.The plurality of polymeric particles of claim 5 wherein thealkaline-earth metal oxide-containing particles cover 2 to 30 percent ofthe outer surface of the shell of the gas-filled polymericmicroelements.